Photographic materials capable of giving high quality original reproduction, stable development baths and simplified replenishment system are required in the field of photomechanical plate making for dealing with the wide variety of diversified and complicated printing forms.
Original documents to be subjected to line work camera processes in particular comprise phototypeset letters, hand written letters, illustrations and halftone dot image photographs. Hence, the original documents for these processes include a mixture of images having different densities and line widths. There is therefore a demand for photomechanical process cameras, photographic materials and image forming methods capable of accurately copying these original documents. On the other hand, enlargement (spread) or reduction (choke) of dot image photographs is widely used in plate making for catalogues and posters and in plate making where screen dots are enlarged In such processes, the number of lines becomes coarser and blurred dots are photographed. With reduction the number of lines per inch is greater than on the original document and finer dots are photographed. Hence, there is a demand for a method of forming images which has a wider latitude for maintaining the reproducibility of halftone dot image gradation.
Halogen lamps or xenon lamps are used as light sources for photomechanical process cameras. Photographic materials are normally ortho sensitized to increase photographic sensitivity to these light sources. However, ortho sensitized photographic materials are greatly affected by chromatic aberration of lenses which is likely to result in deterioration of picture quality. This deterioration is more pronounced with xenon lamp light sources.
Known systems addressing the demand for a wider latitude include those in which line images or halftone dot images containing a clear distinction between image parts and non-image parts and ficturing high contrast and high black densities are obtained by processing lith type silver halide photosensitive materials comprising silver chlorobromides (in which the silver chloride content is at least 50%) in hydroquinone developers having a very low effective concentration of sulfite ion (normally less than 0.1 mol/liter). However, with these methods the developer is very unstable to aerial oxidation because of its low sulfite concentration, and various endeavors and devices have been used to maintain a stable bath activity. At the present time, however, processing is very slow and operational efficiency is low.
Consequently, a demand has arisen for an image forming system in which the instability of image formation with development methods such as those mentioned above (lith development systems) are overcome, with which development is carried out in processing baths having good storage stability, and with which ultra-high contrast photographic characteristics can be realized. The systems in which ultra-high contrast images having a gamma value exceeding 10 are formed by processing surface latent image type silver halide photographic materials to which specified acylhydrazine compounds have been added in development baths of a pH from 11.0 to 12.3 and containing at least 0.15 mol/liter of sulfite preservative and which have good storage stability as suggested in U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606 and 4,311,781. A distinguishing feature of these novel image forming systems is that, silver iodobromides and silver chloroiodobromides can be used, whereas only silver chlorobromides which had a high silver chloride content could be used in the conventional ultra-high contrast image forming systems.
The above mentioned image forming systems provide excellent sharp screen dot quality, processing stability, processing speed and original reproduction properties. But systems which provide improved original reproduction properties have become desirable for dealing with the diversity of printed matter.
On the other hand, operating efficiency is improved when plate assembly and dot-to-dot processes are carried out in a light environment. Consequently, development of photographic materials for plate making purposes which can be handled in environments known as light-rooms and the development of exposure printers has been conducted.
The photographic materials for use in a light-room described herein are photographic materials which can be used safely for long periods of time using light of a wavelength essentially greater than 400 nm, but which does not contain an ultraviolet component as a safe-light.
The photographic materials for use in a light-room which can be used for plate assembly and dot-to-dot processes are photographic materials which are used to carry out negative image/positive image or positive image/positive image conversion, where developed and processed films on which letters and halftone dot images have been formed are used as originals, and a contact exposure is made with a dot-to-dot working photographic material. However, it is desirable (1) that the material performs so that halftone dot images, line images, and letter images may be negative image/positive image converted in accordance with the halftone dot areas and the line width or with letter image width, and (2) that the material performs so that the tone control of the halftone dot images and the line width control of the letter line images is possible. Photographic materials for light-room dot-to-dot work have been supplied in response to these requirements.
However, in the advanced image conversion operation known as super-imposed letter image formation by dot-to-dot work there is the disadvantage that, in comparison with the methods in which dark-room dot-to-dot work is carried out with conventional dark-room dot-to-dot photosensitive materials, there is an inevitable deterioration in the quality of the super-imposed letter image when the light-room dot-to-dot process is used with existing light-room photosensitive materials.
The method of super-imposed letter image formation by dot-to-dot work is described in greater detail below in connection with the sole Figure of this specification. As shown in the Figure, transparent or translucent supports (a) and (c) (generally, polyethylene terephthalate film having a thickness of approximately 100 microns is used) are attached to a letter or line image-containing film (line original) (b) and a halftone dot image-containing film (halftone original) (d), respectively, to form a combined original, and a dot-to-dot working photographic material (e) is brought into contact with the halftone original (d) so that the emulsion surface of the material (e) faces and contacts the halftone image surface of the original (d). Then the material is exposed to light through the combined original by contact exposure.
After exposure, the material is subjected to development processing, and the transparent parts of the line image are formed in a halftone dot image.
The important aspect of this method of forming a super-imposed letter image is that it is ideal for carrying out negative image/positive image conversion in accordance with the halftone dot area and the image width of the halftone dot original and the line original, respectively. However, as shown in the Figure, the halftone dot original is in direct contact with the emulsion surface of the dot-to-dot photographic material when the exposure is made. On the other hand, the line original is exposed to the dot-to-dot photographic material through the intervening support (c) and the halftone dot original (d).
Consequently, when an exposure which provides faithful negative image/positive image conversion of the halftone dot original is given, the image width in the transparent parts of the line image is inevitably reduced since the line original is exposed with blurring through the support (c) and the halftone dot original (d). This is the cause of the inevitable deterioration in quality of the super-imposed letter image.
Systems in which hydrazines are used to overcome the problem described above are disclosed in JP-A-62-80640, JP-A-62-235938, JP-A-62-235939, JP-A-63-104046, JP-A-63-103235, JP-A-63-2906031, JP-A-63-314541 and JP-A-64-13545 (the term "JP-A" as used herein signifies an "unexamined published Japanese patent application"). But these systems cannot be said to be satisfactory and further improvement is desirable.
The use of redox compounds which can release development inhibitors on oxidation is disclosed in JP-A-61-213847, U.S. Pat. No. 4,684,604, JP-A-64-72140 and JP-A-64-72139.
However, various problems arise when these redox compounds are used in negative type ultra-high contrast photographic materials which contain hydrazine derivatives and so the potential of these redox compounds cannot be realized satisfactorily.
Specifically, there is a loss of contrast, and adequate improvement in original reproducibility is not attained.